This invention relates to hydraulic door closer apparatus, and more particularly, to hydraulic door closer apparatus having a novel fluid seal construction. In general, this invention relates to the type of hydraulic door closer apparatus disclosed in U.S. Pat. No. 4,019,220, issued Apr. 26, 1977 to Sidney Lieberman, and assigned to the assignee of the present application, and U.S. Pat. No. 3,426,382, issued Feb. 11, 1969 to T. R. Lasier et al., in which a spring-urged hydraulic piston is arranged to bias a door to its closed position with appropriate hydraulic damping. Typically, in the use of apparatus of this sort, the force generated by a spring is transmitted between the door closer and, depending upon where the door closer is mounted, either a door or door frame. For this purpose, it is usual to provide a linkage consisting of a pair of links, coupled to the door closer and to the door or door frame, as the case may be.
As in the patents referred to above, a rack and pinion arrangement is used to convert the linear motion of the piston within the door closer to rotary or oscillatory motion of an output shaft and the linkage.
Upon opening of the door, the piston is driven by the pinion against the bias of a return spring and against fluid resistance provided by hydraulic circuitry within the device. The hydraulic circuitry is usually made adjustable to provide for variable cushioning or a "back-check" effect as the door approaches the limits of its swing toward the open position. Movement of the door toward the closed position is accomplished by unloading of the return spring, with the speed of closing controlled by damping provided by the hydraulic circuitry.
Since the housing for hydraulic door closers of the above-described type contains hydraulic fluid under pressure, the retention of that fluid free from leakage is an important design requirement. Of particular concern from the standpoint of service life has been the dynamic seal between the housing and the rotary output shaft. Such seals are expected to withstand many thousands of cycles of operation without failure (failure being defined as detectable fluid leakage), and they must do so notwithstanding the potentially degrading effects of wear and age, dust and other external contaminants, contaminants in the hydraulic fluid, variations in ambient and operating temperatures, and wear between moving parts.
With reference to the above mentioned patent to Lasier et al., one shaft sealing technique which has conventionally been used involves the resilient sealing device known as an "O-ring". O-ring seals, which are conventionally used in both rotary and recipricatory applications, use a resilient sealing member or O-ring, usually circular in transverse cross-section, loosely associated with a straight-sided annular groove having a height and width corresponding approximately to the dimensions of the sealing member but not conforming to its cross-section. In such devices, as is well known, dynamic and static pressure in the working fluid causes the sealing member to deform and press against the groove and adjacent working parts to provide the desired sealing effect. Thus, the O-ring, by virtue of its inherent characteristic, reacts and accommodates itself to variations in pressure and irregularities in the surfaces of the member or members against which it works.
O-rings are deceptively simple in appearance, and experience with them as shaft seals for door closers has shown that in a percentage of cases, O-rings apparently regular in appearance will nevertheless prove, in conventional seal structures, to permit leakage. It has also been found with conventional constructions that in a demonstrable fairly constant percentage of assemblies, failure will occur within a relatively small number of cycles of operation.
The present invention relates to a door closer construction in which O-rings are used for shaft sealing purposes, but in which the useful life of the seal is greater than in conventional constructions and the seal is less sensitive than conventional constructions to O-ring condition.
The foregoing and other objects of this invention are realized, in the presently preferred form of the invention by a shaft seal in which the output shaft of a door closer is supported in the housing of the door closer by bearings at both ends. The bearings and packing nuts associated with them provide an annular chamber or groove for multiple O-rings, preferably a pair of O-rings.
It is recognized that some of the advantage of the present invention may result from the fact that one of the preferred pair of O-rings merely serves as a backup to the other, the probability of both being grossly defective being extremely small. Surprisingly, however, it has been found in testing examples of the present invention, that use of two O-rings, each of which permits leakage in a conventional O-ring seal can nevertheless provide a reliable leak-free seal.